There are services (23andme, AncestryDNA) that will associate an ethnic group to you from your spit. Could non-coding DNA in theory be useful for this goal i.e. are there statistically meaningful differences in non-coding DNA between different ethnic groups?
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2$\begingroup$ We only deal with one question per post. The first would be about the standards applied in a test by a commercial service - this would likely be off-topic here as it could be seen as promotion of that service. The second might be on-topic , but you would need to show what researches you'd done on the topic and where you'd gotten stuck. (Personally I'm interested in the answer should it be different from expected heritable differences by a significant amount). You should take our tour and refer to the help center for guidance to our ways - then edit the question to show your workings. $\endgroup$– Jiminy Cricket.Commented Oct 30, 2021 at 11:29
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$\begingroup$ This answer links to the site of 23andme biology.stackexchange.com/a/7295/68099 $\endgroup$– fielanbCommented Oct 30, 2021 at 11:35
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1$\begingroup$ Well then, perhaps it would be on-topic - but beware, that's from 2013 and the site-rules have significantly tightened since then - I'll let those with greater familiarity with this site on the stack tell you the current policy. (A cursory search of our meta didn't enlighten me on the subject). You would still need to show your researches into the remaining topic. $\endgroup$– Jiminy Cricket.Commented Oct 30, 2021 at 11:42
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1$\begingroup$ Personally I see nothing wrong with discussing particular direct to consumer genetic testing companies. $\endgroup$– user438383Commented Oct 30, 2021 at 12:04
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2 Answers
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Not only 'in theory', but it is used for ancestry testing.
Coding DNA (exonic regions) tend to be more highly conserved between individuals, as changes to the sequence are more likely to have a deleterious effect on an important phenotype (think a mutation which makes someone only have a single arm). Non-coding DNA is less constrained by selection and varies more between individuals / ethnic groups. This makes it more useful for identifying variants specific to different ethnicities, which makes the basis of ancestry testing. Typically in ancestry testing SNPs which show evidence of being under some kind of functional selection (i.e. are out of Hardy-Weinberg equilibrium) are excluded from the analysis. Neutrally evolving SNPs (which are more likely to be found in non-coding regions) are more likely to reflect the true population phylogeny.
I'll try and update this post with some references.
answered Oct 30, 2021 at 11:55
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$\begingroup$ But when people try to determine someone's ethnicity by looking at them they are relying on information (eyes, cheekbones, skin color, fat level, lip size, height etc.) primarily shaped by coding DNA right? $\endgroup$– fielanbCommented Oct 30, 2021 at 20:43
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2$\begingroup$ @fielanb The differences that you note between people of different ancestry groups are largely red herrings. They give a superficial impression of difference (which in some cases does not have a clear genetic basis), relative to overwhelming similarity in functional regions of DNA (nyti.ms/3CxBxcj, nature.com/articles/ng1456). Noncoding regions on the other hand tend to yield a reasonable historical record of population differentiation, because they are not functionally constrained, and mutations in regions without functions are therefore more likely to be passed on. $\endgroup$ Commented Oct 30, 2021 at 22:02
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user438383's answer is correct. Non-coding DNA is much more useful for ancestral research, especially of ancient ancestry, because it preserves mistakes or changes that would damage a person if they occurred in coding DNA. For this reason people have SNP's in their DNA that date back thousands of years. By comparing and contrasting SNPs it can be determined absolutely how different people are related to each other. We are all related to each other, the only question is how far back you have to go to find the relation.
Concerning physical characteristics like eye and hair color, those are indeed determined by coding DNA, but are what are called "expressed traits" which means that how they get expressed is complex and depends on random factors. For example, I have seen a clone of a cat where the original was completely black, but the clone had a white patch on its chest. However, a littermate of the original did have the same patch. So, you see the gene codes for black, but when the organism grows in the environment, random differences can occur. Part of this is due to a process called "methylation". When a zygote is developed, the egg's genetic material is methylated and this inactivates or activates genes randomly (see "Methylation dynamics during the maternal-to-zygotic genome transition in dioecious species" Willian T. A. F. Silva for more information), thereby causing differences in physical makeup of the organism. Note that a person has many different copies of the same gene which can differ from each other, so which particular gene gets activated will affect the final form of the organism.
Physical characteristics can be a clue to a genetic heritage, but it is important to realize that for every gene that gets expressed many more are latent and go unused, perhaps to surface in a later generation.
answered Oct 30, 2021 at 23:54
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$\begingroup$ The classic reference for reaction norms (gene x environment interaction) would be Lewontin 1974 (here is a republished version that is easy to access: pubmed.ncbi.nlm.nih.gov/16645033). $\endgroup$ Commented Oct 31, 2021 at 21:31